Atomic deletion of database data categories

ABSTRACT

A device maintains, in a database, a plurality of data items, each data item of the plurality of data items being associated with a respective category. The device associates, in the database, a first counter value with each data item, the first counter value indicating a number of times the respective category has been deleted from the database at a time when the data item was stored in the database. The device associates, in the database or another database, a second counter value with the respective category, the second counter value indicating a current value for a number of times the respective category has been deleted from the database. The device selectively deletes, from the database, one or more data items of the plurality of data items from the database based on the first counter values and the second counter value.

BACKGROUND

Database management systems (DBMSs) organize the storage of data. DBMSscontrol the creation, maintenance and use of data structures stored intheir databases. Database data structures are typically stored in memoryor on hard disk in one of many forms, including ordered or unorderedflat files, heaps, hash buckets, B+ trees or Indexed Sequential AccessMethod (ISAM) structures. Databases typically conduct databasetransactions by enforcing one or more of four rules: atomicity,consistency, isolation and durability. The atomicity rule requires thatall tasks in a transaction must be performed, or that none of the tasksin the transaction should be performed. The consistency rule requiresthat every transaction preserves the integrity constraints of thedatabase. The isolation rule requires that two simultaneous transactionsnot interfere with one another (i.e., intermediate results within atransaction are not visible to other transactions). The durability rulerequires that completed transactions not be aborted or their resultsdiscarded.

Interface for Metadata Access Points (IF-MAP) is a protocol thatprovides a standardized framework for network and security devices topublish device data, such as, for example, Internet Protocol (IP)address or authentication data, to a central repository that can be usedby other applications. The central repository can be used for security,asset management, discovery, or other purposes. The central repository,thus, acts as a DBMS that manages data related to network and securitydevices. Data published to the IF-MAP repository may be labeled with anidentifier of the publisher that published the data to the repository.The IF-MAP protocol then permits a publisher to subsequently purge(i.e., delete) previously published material using, for example, apurgePublisher request. Data from the repository labeled with thepublisher's identifier must be deleted in response to the issuance of aIF-MAP purgePublisher request. A publisher may desire to purge publisheddata due to, for example, a system failure, a system re-start or anetwork disconnection event associated with the publisher.

SUMMARY

In accordance with one embodiment, a method may include maintaining, ina database, a plurality of data items, each data item of the pluralityof data items being associated with a respective category. The methodmay further include associating, in the database, a first counter valuewith each data item, the first counter value indicating a number oftimes the respective category has been deleted from the database at atime when the data item was stored in the database. The method may alsoinclude associating, in the database, a second counter value with therespective category, the second counter value indicating a current valuefor a number of times the respective category has been deleted from thedatabase. The method may additionally include selectively deleting, fromthe database, one or more data items of the plurality of data items fromthe database based on the first counter values and the second countervalue.

In another implementation, a device may include a memory to storeinstructions; and a processor to execute the instructions to: maintain,in a database, a plurality of data items, each data item of theplurality of data item being associated with a respective category,associate, in the database, a first counter value with each data item,the first counter value indicating a number of times the respectivecategory has been deleted from the database at a time when the data itemwas stored in the database, associate, in the database, a second countervalue with the respective category, the second counter value indicatinga current value for a number of times the respective category has beendeleted from the database, receive a request to delete the category,increment the second counter value, in response to receiving thedeletion request, to generate an incremented second counter value, andselectively delete, from the database, one or more data items of theplurality of data items based on the first counter values and theincremented second counter value.

In still another implementation, a computer-readable medium containinginstructions executable by at least one processor may include one ormore instructions to maintain, in a database, a plurality of data items,each data item of the plurality of data item being associated with arespective category. The computer-readable medium may further includeone or more instructions to associate, in the database, a first countervalue with each data item, the first counter value indicating a numberof times the respective category has been deleted from the database at atime when the data item was stored in the database. Thecomputer-readable medium may also include one or more instructions toassociate, in the database, a second counter value with the respectivecategory, the second counter value indicating a current value for anumber of times the respective category has been deleted from thedatabase. The computer-readable medium may additionally include one ormore instructions to selectively delete, from the database, one or moredata items of the plurality of data items from the database based on thefirst counter values and the second counter value.

In yet another implementation, a device may include means formaintaining, in a database, a plurality of data items, each data item ofthe plurality of data item being associated with a respective category.The device may further include means for associating, in the database, afirst counter value with each data item, the first counter valueindicating a number of times the respective category has been deletedfrom the database at a time when the data item was stored in thedatabase, and means for associating, in the database, a second countervalue with the respective category, the second counter value indicatinga current value for a number of times the respective category has beendeleted from the database. The device may also include means forreceiving a request to delete the category, where the deletion requestcomprises an Interface for Metadata Access Points (IF-MAP)purgePublisher request, and means for incrementing the second countervalue, in response to receiving the deletion request, to generate anincremented second counter value. The device may additionally includemeans for selectively deleting, from the database, one or more dataitems of the plurality of data items from the database based on thefirst counter values and the incremented second counter value.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more embodiments describedherein and, together with the description, explain the invention. In thedrawings,

FIG. 1A is a diagram of an exemplary network in which systems andmethods described herein may be implemented;

FIG. 1B is a diagram of exemplary interactions between a client and thedata access point of FIG. 1A;

FIG. 2 is a diagram of components of an exemplary device that maycorrespond to the clients and/or data access point of FIG. 1B;

FIG. 3 is a diagram of a first exemplary table that may be stored in thedatabase of FIG. 1A;

FIG. 4 is a diagram of a second exemplary table that may be stored inthe database of FIG. 1A;

FIG. 5 is a flow chart that illustrates an exemplary process forcategorizing and storing an item of data in the database of FIG. 1A;

FIG. 6 is a flow chart that illustrates an exemplary process forreceiving a category deletion request and for performing garbagecollection with respect to data stored in the database of FIG. 1A;

FIG. 7 is a flow chart that illustrates an exemplary garbage collectionprocess for deleting data stored in the database of FIG. 1A; and

FIG. 8 is a flow chart that illustrates an exemplary process forresponding to an item query received at the data access point of FIG.1A.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings.The same reference numbers may be used in different drawings to identifythe same or similar elements. Also, the following detailed descriptiondoes not limit the invention. Instead, the scope of the invention isdefined by the appended claims and equivalents.

Exemplary embodiments described herein implement mechanisms foratomically deleting categories of data from a database. As describedherein, a counter value, which maintains a current count representingthe quantity of times a given category has been deleted, is used whendeciding whether to delete items of data that are associated with thecategory. A category, as referred to herein, includes a label thatidentifies a set of related data items. When a new item of data isreceived for storing in the database, where the item of data isassociated with a category, a current count, representing the quantityof times that a particular category has been deleted, is incremented andthe new value is stored in the database. Individual data items may thenbe selected for deletion from the database by comparing the new value ofthe count, that represents the quantity of times that the category hasbeen deleted, with the previously stored count associated with each itemof data. Subsequently, when a deletion request is received for thecategory, a current count, representing the quantity of times that thecategory has been deleted, is obtained at that particular instant intime, and compared to the previously stored count associated with theitem of data. If the current count is greater than the previously storedcount, then the item of data may be deleted from memory during a garbagecollection process. This garbage collection process may be repeated foreach data item stored in the memory that is associated with the samecategory.

Exemplary Network

FIG. 1A depicts an exemplary network 100 in which systems and methodsdescribed herein may be implemented. Network 100 may include multipleclients 110-1 through 110-N, a network 120, a data access point 130, anda database 140. Clients 110-1 through 110-N, and data access point 130,may connect to network 120 via wired or wireless links

Each of clients 110-1 through 110-N (collectively referred to herein as“clients 110,” or generically referred to herein as “client 110”) mayinclude a server (e.g., a rack mounted server), a computer (e.g.,laptop, desktop or palmtop), a cellular radiotelephone, a personaldigital assistant (PDA), or a Personal Communications Systems (PCS)terminal. In some embodiments, one or more of clients 110 may include aserver entity that may interact with data access point 130 via network120.

Network 120 may include one or more networks of any type, including alocal area network (LAN); a wide area network (WAN); a metropolitan areanetwork (MAN); a telephone network such as a Public Switched TelephoneNetwork (PSTN) or a Public Land Mobile Network (PLMN); a satellitenetwork; an intranet; the Internet; or a combination of networks. ThePLMN may further include a packet-switched network, such as, forexample, a General Packet Radio Service (GPRS) network, a CellularDigital Packet Data (CDPD) network, or a Mobile IP network.

Data access point 130 may include a server entity or device that mayreceive update requests from clients 110-1 through 110-N for storingdata items in database 140. Upon receipt of such update requests, dataaccess point 130 may store the requested data item(s) in database 140,as described in further detail below. Data access point 130 may furtherreceive query requests for accessing data items stored in database 140.Upon receipt of such requests, data access point 130 may access andretrieve the requested data item(s) from database 140 and return them tothe requesting one of clients 110. Data access point 130 may alsoreceive category deletion requests from clients 110-1 through 110-N.Upon receipt of a category deletion request, data access point 130 maydelete data items from database 140 that correspond to the category thathas been requested to be deleted.

Database 140 may include any type of existing database that may storedata for retrieval by data access point 130. Data access point 130 may,for example, interact with database 140 to store data items receivedfrom clients 110-1 through 110-N, may retrieve previously stored dataitems from database 140, and may delete data items associated with oneor more categories.

The number of devices depicted in FIG. 1A is exemplary. Fewer, or more,devices than those shown may be included in network 100. Operationsdescribed herein as being performed by one device in network 100 may beperformed by one or more other devices.

FIG. 1B graphically depicts exemplary interactions between a client(e.g., client 110-1) and data access point 130. As shown, client 110-1may publish 150 a data item(s) to data access point 130. Publishing of adata item(s) to data access point 130 enables data access point 130 tostore the data item(s) in database 140 for modification and/or retrievalby any of clients 110-1 through 110-N. Client 110-1 may further send adata query 160 to data access point 130 for retrieving a specific dataitem(s) from database 140. Client 110-1 may also send a categorydeletion request 170 to data access point 130 for deleting an entirecategory of data items stored in database 140. In an embodiment in whichdatabase 140 is serving as an IF-MAP repository, a given category mayinclude an identifier of the publisher that published the data item(s)to the repository (e.g., a unique identifier of a respective one ofclients 110). In such an IF-MAP embodiment, the category deletionrequest may correspond to an IF-MAP purgePublisher request.

Interactions, other than those shown in FIG. 1B, may occur betweenclients 110 and data access point 130.

Exemplary Network Device

FIG. 2 is a diagram of components of a device 200 according to anexemplary embodiment. Device may correspond to each of clients 110-1through 110-N, and data access point 130. Device 200 may include a bus210, a processor 220, a main memory 230, a read only memory (ROM) 240, astorage device 250, input device(s) 260, output device(s) 270, and acommunication interface 280. Bus 210 may include a path that permitscommunication among the components of device 200.

Processor 220 may include, for example, a processor, microprocessor,and/or processing logic that may interpret and execute instructions. Insome implementations, processor 220 may include multiple processors(e.g., parallel processors). Main memory 230 may include a random accessmemory (RAM) or another type of dynamic storage device that may storeinformation and instructions for execution by processor 220. ROM 240 mayinclude a ROM device or another type of static storage device that maystore static information and instructions for use by processor 220.Storage device 250 may include a magnetic and/or optical recordingmedium and its corresponding drive. Storage device 250 may furtherinclude a solid state drive.

Input device(s) 260 may include one or more mechanisms that permit anoperator to input information to device 200, such as a keyboard, amouse, a pen, voice recognition and/or biometric mechanisms, etc. Outputdevice(s) 270 may include one or more mechanisms that output informationto the operator, including a display, a printer, a speaker, etc.Communication interface 280 may include any transceiver-like mechanismthat enables device 200 to communicate with other devices and/orsystems. For example, communication interface 280 may include mechanismsfor communicating with another device or system via network 120.

Device 200 may perform certain operations or processes, as will bedescribed in detail below. Device 200 may perform these operations inresponse to processor 220 executing software instructions contained in acomputer-readable medium, such as memory 230. A computer-readable mediummay be defined as a physical or logical memory device. A logical memorydevice may include memory space within a single physical memory deviceor spread across multiple physical memory devices.

The software instructions may be read into memory 230 from anothercomputer-readable medium, such as storage device 250, or from anotherdevice via communication interface 280. The software instructionscontained in memory 230 may cause processor 220 to perform operations orprocesses that will be described later. Alternatively, hardwiredcircuitry may be used in place of or in combination with softwareinstructions to implement processes consistent with the principles ofthe invention. Thus, exemplary implementations are not limited to anyspecific combination of hardware circuitry and software.

Exemplary Data Item Table

FIG. 3 illustrates a data item table 300 according to an exemplaryembodiment. Data item table 300 may be stored in database 140. Data itemtable 300 may include multiple entries 310, each of which may include adata item field 320, and an item deletion count field 340. Entries 310may include additional, and/or different, fields than those depicted inFIG. 3.

Data item field 320 may store a specific item of data received from aclient 110. The item of data may include any type of data. For example,the item of data may include any type of data published using the IF-MAPprotocol, such as information about other equipment and users in thenetwork published by a client 110. In one implementation, client 110 mayinclude a login server that decides whether to permit another computerto log-in to a network, and subsequently publishes information about thelog-in computer (or the user of the log-in computer). A category may beassociated with each corresponding data item stored in item field 320.The category may, for example, identify a set of related data items. Inan IF-MAP protocol embodiment, for example, the category may include anidentifier of the publisher, which published the data item stored initem field 320, to database 140. One or more items of data stored initem fields 320 of table 300 may, therefore, be associated with acategory. Item deletion count field 340 may include a count of how manytimes a category had been deleted at a point in time in which the dataitem stored in item field 320 was received for storage in table 300. Insome embodiments (not shown), there may be several versions of a samedata item, with each version being labeled with a different value initem deletion count field 340.

Exemplary Category Table

FIG. 4 illustrates a category table 400 according to an exemplaryembodiment. Category table 400 may be stored in database 140. Categorytable 400 may include multiple entries 410, each of which may include acategory field 420 and a category deletion count field 430. Entries 410may include additional, and/or different, fields than those depicted inFIG. 3.

Category field 420 may store an identifier that identifies a category ofdata stored in database 140. Each category may identify a set of relateddata items that are stored in a respective item field 320 of table 300.Category deletion count field 430 may store a value representing thequantity of times the category, identified in category field 420 of acorresponding entry 410, has been deleted. Each time a deletion requestis received for a category identified in category field 420, a countervalue, stored in category deletion count field 430, may be incremented.

Exemplary Process for Categorizing and Storing an Item of Data

FIG. 5 is a flow chart that illustrates an exemplary process forcategorizing and storing an item of data received by data access point130 from a client 110. The exemplary process of FIG. 5 may beimplemented by data access point 130. In other embodiments, some or allof the blocks described below may be performed by another device or acombination of devices.

The exemplary process may include receiving an item of data (block 500).For example, as shown in FIG. 1B, data access point 130 may receive apublish request 150 that includes an item of data to be published (i.e.,stored and made available to clients 110-1 through 110-N) in database140. One of clients 110 may send publish request 150 to data accesspoint 130 via network 120.

A category of the received item of data may be determined (block 510).The category of the received data item may be determined by extractingdata from the data item, or from data related to the data item, or bycomputing a function of the data item. The function may include any typeof function that may operate upon the data item to compute a category.In some embodiments, the category of the received item of data may beextracted from the publish request 150 received from a client 110. In anIF-MAP embodiment, for example, publish request 150 may include apublisher identifier (ID) that identifies client 110 that sent the itemof data for storage, and this publisher ID may be extracted from publishrequest 150 and used as the category of the received item of data.

A current count that represents a number of times that the category hasbeen deleted may be obtained and set as an item deletion count for theitem of data (block 520). The category determined in block 510 may bematched with a category stored in category field 420 of table 400. Acategory deletion count from field 430 of the entry 410, in which thematching category field 420 is identified, may be retrieved from table400. The retrieved category deletion count may then be set as the itemdeletion count for the item of data.

The item of data may be labeled with the obtained item deletion count(block 530). In one embodiment, the labeling may include storing theobtained deletion count in the corresponding item deletion count 340 oftable 300.

Exemplary Category Deletion and Garbage Collection Process

FIGS. 6 and 7 are flow charts that illustrate an exemplary process fordeleting a category and for performing garbage collection. The exemplaryprocess of FIGS. 6 and 7 may be implemented by data access point 130. Inother embodiments, some or all of the blocks described below may beperformed by another device or a combination of devices.

The exemplary process may include receiving a deletion request for anidentified category (block 600). A client 110 may send a deletionrequest, which identifies a particular category, to data access point130 via network 120. Referring to FIG. 1B, for example, client 110-1 maysend category deletion request 170 to data access point 130. Categorydeletion request 170 may include an identifier of a category. In oneembodiment, the category identifier may include a unique identifierassociated with client 110 that published the data items that arealready associated with the category in database 140. Additionally, thedeletion request may occur when it is determined that data access point130 has lost contact with one of clients 110-1 through 110-N. Upon aloss of contact with one of clients 110-1 through 110-N, a deletionrequest may be considered to have been received by data access point 130for a corresponding category.

The identified category's deletion count may be incremented (block 610).Table 400 may be searched to identify an entry, where the identifier incategory field 420 matches the category identifier contained in thedeletion request. The corresponding category deletion count field 430for the entry may be retrieved, incremented, and then re-stored in thesame category deletion count field 430.

Garbage collection may be performed (block 620). The garbage collectionprocess may traverse through stored data items in table 300 to compareeach data item's item deletion count with the count value stored in theidentified category's category deletion count 430. If the comparisonindicates that the count value stored in the identified category'scategory deletion count field 430 is greater than the data item's countvalue stored in the item deletion count field 340, then the data itemmay be deleted from table 300. Further exemplary details of the garbagecollection process are described below with respect to FIG. 7.

The garbage collection process may begin with the identification of anext stored data item (block 700). During the first occurrence of block700 in the garbage collection process, the next stored data item may bea first data item stored in database 140. Various techniques may be usedfor identifying a data item in table 300. In one embodiment, table 300may be sequentially searched to process each stored data itemcorresponding to an entry 310. In another embodiment, table 300 may beindexed by category, so that members of a category that have had theirdeletion counts incremented can be found relatively quickly.

The data item's category and item deletion count may be determined(block 710). The contents of item deletion count field 340 of the dataitem identified in block 700 may be retrieved from table 300. Thecategory of the data item identified in block 700 may be determined byextracting data from the data item, or from data related to the dataitem, or by computing a function of the data item. The function mayinclude any type of function that may operate upon the data item tocompute a category (i.e., the same function used in block 510 above). Insome embodiments, the category of the received item of data may beextracted from the original publish request 150 received from a client110. In an IF-MAP embodiment, for example, publish request 150 mayinclude a publisher identifier (ID) that identifies client 110 that sentthe item of data for storage, and this publisher ID may be extractedfrom publish request 150 and used as the category of the received itemof data. The category's category deletion count may be obtained (block720). The determined category from block 710 may be used to identify amatching category in an entry 410 in category field 420 of table 400.The contents of the corresponding category deletion count field 430 maythen be retrieved.

A determination may be made whether the obtained category deletion countis greater than the item deletion count (block 730). A comparison may bemade between the counter value stored in item deletion count field 340retrieved in block 710 and the counter value stored in category deletioncount field 430 retrieved in block 720. If the category deletion countis greater than the item deletion count (block 730—YES), then the itemof data may be deleted (block 750). For example, if the counter valuestored in the category deletion count field 430 retrieved in block 720is greater than the counter value stored in the item deletion countfield 340 retrieved in block 710, then the corresponding data itemstored in item field 320 may be deleted, along with fields 330 and 340.The exemplary process may then continue at block 740.

It may be determined whether there are more data items remaining (block740). If there are no more data items remaining (block 740—NO), then theexemplary process may end. If there are more data items remaining (block740—YES), then the exemplary process may continue at block 700 with theidentification of a next stored data item.

The exemplary process of blocks 700 through 750 may be repeated for eachdata item stored in table 300. Subsequent to completion of blocks700-750 for each data item in table 300, the garbage collection processof block 620 may complete to finish the exemplary deletion requestprocess of FIG. 6.

Exemplary Item Query Process

FIG. 8 is a flow chart that illustrates an exemplary process forreceiving an item query from client 110. The exemplary process of FIG. 8may be implemented by data access point 130. In other embodiments, someor all of the blocks described below may be performed by another deviceor a combination of devices.

The exemplary process may include the receipt of an item query (block800). A client 110 may send an item query to data access point 130 toseek to retrieve a specific data item(s) from database 140. An itemdeletion count for the queried item may be retrieved (block 810). Thedata item identified in the item query may be compared to the content ofitem fields 320 in table 300 to identify an entry 310 of table 300 whosecontent matches this item. The contents of the corresponding itemdeletion count 340, of the identified entry 310, may then be retrieved.A category for the data item may be determined (block 820). The categoryof the data item may be determined by extracting data from the dataitem, or from data related to the data item, or by computing a functionof the data item. The function may include any type of function that mayoperate upon the data item to compute a category.

A current category deletion count for the determined category may beretrieved (block 830). Table 400 may be searched to locate an entry 410whose category field 420 content matches the contents of category field330 retrieved in block 820. The counter value stored in categorydeletion count field 430 for the identified entry 410 may be retrieved.

The category deletion count and the item deletion count may be compared(block 840). For example, the counter value stored in category deletionfield 430, retrieved in block 830, may be compared with the countervalue stored in item deletion count field 340, retrieved in block 810.

If the comparison of block 840 indicates that the category deletioncount is less than or equal to the item deletion count (block 850-YES),then the queried data item may be retrieved and returned (block 860).The contents of item field 320 for entry 310, identified in block 810,may be retrieved and returned to the requesting client 110. If thecomparison of block 840 indicates that the category deletion count isgreater than the item deletion count (block 850-NO), then the querieddata item may be hidden (block 870). A queried data item may be “hidden”by making the data item non-retrievable from table 300 in response to anitem query, even though the queried item may still be stored in table300. However, the queried data item may otherwise be retrievable forother processing until deleted in block 750 of FIG. 7 of the garbagecollection process.

CONCLUSION

As described herein, categories of data may be deleted in an atomicfashion from a database. The atomic category deletion process, asdescribed herein, uses a counter value, which represents a number oftimes that a given category has been deleted, when deciding whether todelete items of data that are associated with a category that is beingprocessed for deletion. The exemplary embodiments described herein maybe applied, for example, to purgePublisher requests in the IF-MAPprotocol, where the categories of data that are deleted correspond tosets of data items that are labeled with a same publisher identifier.

The foregoing description of embodiments described herein providesillustration and description, but is not intended to be exhaustive or tolimit the embodiments described herein to the precise form disclosed.Modifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Forexample, certain portions have been described as executed asinstructions by one or more processing units. However, implementations,other than software implementations, may be used, including, forexample, hardware implementations, such as application specificintegrated circuits, field programmable gate arrays, or combinations ofhardware and software.

While series of blocks have been described in FIGS. 5-8, the order ofthe blocks may vary in other implementations. Also, non-dependent blocksmay be performed in parallel. Even though particular combinations offeatures are recited in the claims and/or disclosed in thespecification, these combinations are not intended to limit theinvention. In fact, many of these features may be combined in ways notspecifically recited in the claims and/or disclosed in thespecification. For example, the isolation rule (i.e., rule that otheroperations cannot access the data in an intermediate state during atransaction) may be implemented in some embodiments. To achieveisolation, every transaction may begin by taking a “point-in-time”snapshot of the item deletion counts (i.e., from item deletion countfield 340), and when a data item is queried from database 140, thesnapshot of the item deletion counts may be used rather than the mostcurrent item deletion counts. In this way, a category deletion thathappens after the “point-in-time” snapshot, but before the transactionfinishes, will not affect the transaction. The transaction may include,for example, an update/publish or a query.

Exemplary embodiments have been described herein with respect to storinga single category and a single item deletion count in association witheach data item in table 300 of database 140. However, in otherembodiments, each item can belong to n categories, where the ncategories form a hierarchy. In such embodiments, when storing a dataitem in table 300, the category is stored in association with the dataitem that is the farthest from the root of the hierarchy. Then, todelete a category, the category's category deletion count isincremented, and the category deletion counts of all the category'sdescendants in the hierarchy are also incremented.

Exemplary embodiments have further been described herein as usingdeletion counts (e.g., item deletion count 340, category deletion count430) for performing garbage collection. In other embodiments, other“monotonic” values (i.e., values that are always increasing) may beused. For example, in one embodiment, monotonic time stamps could beused instead of the deletion counts. In such an embodiment, an itemcould be garbage if its timestamp is greater than the category'stimestamp.

No element, act, or instruction used in the description of the presentapplication should be construed as critical or essential to theinvention unless explicitly described as such. Also, as used herein, thearticle “a” is intended to include one or more items. Where only oneitem is intended, the term “one” or similar language is used. Further,the phrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise. The scope of the invention isdefined by the claims and their equivalents.

1. A method, comprising: maintaining, in a database, a plurality of dataitems, each data item of the plurality of data items being associatedwith a respective category; associating, in the database, a firstcounter value with each data item, the first counter value indicating anumber of times the respective category has been deleted from thedatabase at a time when the data item was stored in the database;associating, in the database or another database, a second counter valuewith the respective category, the second counter value indicating acurrent value for a number of times the respective category has beendeleted from the database; and selectively deleting, from the database,one or more of the data items, of the plurality of data items, from thedatabase based on the first counter values and the second counter value.2. The method of claim 1, further comprising: determining the respectivecategory by extracting data from the data item, or by extracting datafrom data related to the data item.
 3. The method of claim 1, furthercomprising: determining the respective category by computing a functionof the data item.
 4. The method of claim 1, further comprising:receiving, at a data access device, a request to delete the respectivecategory; and incrementing the second counter value, in response toreceiving the deletion request, to generate an incremented secondcounter value, where selectively deleting the one or more data itemsfrom the database is based on the first counter values and theincremented second counter value.
 5. The method of claim 1, furthercomprising: receiving a query for a requested data item of the pluralityof data items; retrieving the first counter value associated with therequested data item; retrieving the second counter value associated withthe respective category; comparing the first counter value with thesecond counter value to produce a first comparison; and selectivelyretrieving and returning the requested data item, or hiding therequested data item for garbage collection, based on the firstcomparison.
 6. The method of claim 5, where comparing the first countervalue with the second counter value comprises: determining if the secondcounter value is less than or equal to the first counter value, andwhere selectively retrieving and returning the requested data item, orhiding the requested data item for garbage collection comprises:retrieving and returning the requested data item if the second countervalue is less than or equal to the first counter value, or designatingthe requested data item for garbage collection, and not retrieving andreturning the data item, if the second counter value is greater than thefirst counter value.
 7. The method of claim 1, where selectivelydeleting the one or more data items from the database comprises:comparing, for one data item of the plurality of data items, the firstcounter value with the second counter value to produce a firstcomparison; and deleting the one data item based on the firstcomparison.
 8. The method of claim 7, where comparing the first countervalue with the first second counter value further comprises: determiningif the second counter value is different than the first counter value;and deleting the one data item when the second counter value isdifferent than the first counter value.
 9. The method of claim 8, wheredetermining if the second counter value is different than the firstcounter value comprises: determining if the second counter value isgreater than the first counter value, and where deleting the one dataitem when the second counter value is different than the first countervalue comprises: deleting the one data item when the second countervalue is greater than the first counter value.
 10. The method of claim1, where the respective category identifies the plurality of data itemsas a set of related data items.
 11. The method of claim 10, where therespective category comprises an identifier associated with a publisherthat originated the plurality of data items.
 12. The method of claim 4,where the deletion request comprises an Interface for Metadata AccessPoints (IF-MAP) purgePublisher request.
 13. A device, comprising: amemory to store instructions; and a processor to execute theinstructions to: maintain, in a database, a plurality of data items,each data item of the plurality of data item being associated with arespective category, associate, in the database, a first counter valuewith each data item, the first counter value indicating a number oftimes the respective category has been deleted from the database at atime when the data item was stored in the database, associate, in thedatabase or another database, a second counter value with the respectivecategory, the second counter value indicating a current value for anumber of times the respective category has been deleted from thedatabase, receive a request to delete the category, increment the secondcounter value, in response to receiving the deletion request, togenerate an incremented second counter value, and selectively delete,from the database, one or more of the plurality of data items based onthe first counter values and the incremented second counter value. 14.The device of claim 13, where the processor is further to execute theinstructions to: determine the respective category by extracting datafrom the data item, or by extracting data from data related to the dataitem.
 15. The device of claim 13, where the processor is further toexecute the instructions to: determine the respective category bycomputing a function of the data item.
 16. The device of claim 13, wherethe processor is further to execute the instructions to: receive a queryfor a requested data item of the plurality of data items, retrieve thefirst counter value associated with the requested data item, retrievethe second counter value associated with the respective category,compare the first counter value with the second counter value to producea first comparison, and selectively retrieve and return the requesteddata item, or designate the requested data item for garbage collection,based on the first comparison.
 17. The device of claim 16, where, whencomparing the first counter value with the second counter value, theprocessor is further to execute the instructions to: determine if thesecond counter value is less than or equal to the first counter value,and where, when selectively retrieving and returning the requested dataitem, or designating the requested data item for garbage collection, theprocessor is further to execute the instructions to: retrieve and returnthe requested data item when the second counter value is less than orequal to the first counter value, or designate the requested data itemfor garbage collection, and not retrieve and return the requested dataitem, when the second counter value is greater than the first countervalue.
 18. The device of claim 13, where, when selectively deleting thedata items from the database, the processor is further to: compare thefirst counter value, associated with one data item of the plurality ofdata items with the second counter value to produce a first comparison;and delete the one data item based on the first comparison.
 19. Thedevice of claim 18, where, when comparing the first counter value withthe second counter value, the processor is further to: determine if thesecond counter value is different than the first counter value; anddelete the one data item when the second counter value is different thanthe first counter value.
 20. The method of claim 19, where, whendetermining if the second counter value is different than the firstcounter value, the processor is further to: determine if the secondcounter value is greater than the first counter value, and where, whendeleting the one data item when the second counter value is differentthan the first counter value, the processor is further to: delete theone data item when the second counter value is greater than the firstcounter value.
 21. The method of claim 13, where the respective categoryidentifies the plurality of data items as a set of related data items.22. The method of claim 21, where the respective category comprises anidentifier associated with a publisher that originated the plurality ofdata items.
 23. The method of claim 13, where the deletion requestcomprises an Interface for Metadata Access Points (IF-MAP)purgePublisher request.
 24. A computer-readable medium containinginstructions executable by at least one processor, the computer-readablemedium comprising: one or more instructions to maintain, in a database,a plurality of data items, each data item of the plurality of data itembeing associated with a respective category; one or more instructions toassociate, in the database, a first counter value with each data item,the first counter value indicating a number of times the respectivecategory has been deleted from the database at a time when the data itemwas stored in the database; one or more instructions to associate, inthe database or another database, a second counter value with therespective category, the second counter value indicating a current valuefor a number of times the respective category has been deleted from thedatabase; and one or more instructions to selectively delete, from thedatabase, one or more data items of the plurality of data items from thedatabase based on the first counter values and the second counter value.25. A device, comprising: means for maintaining, in a database, aplurality of data items, each data item of the plurality of data itembeing associated with a respective category; means for associating, inthe database, a first counter value with each data item, the firstcounter value indicating a number of times the respective category hasbeen deleted from the database at a time when the data item was storedin the database; means for associating, in the database or anotherdatabase, a second counter value with the respective category, thesecond counter value indicating a current value for a number of timesthe respective category has been deleted from the database; means forreceiving a request to delete the category, where the deletion requestcomprises an Interface for Metadata Access Points (IF-MAP)purgePublisher request; means for incrementing the second counter value,in response to receiving the deletion request, to generate anincremented second counter value; and means for selectively deleting,from the database, one or more data items of the plurality of data itemsfrom the database based on the first counter values and the incrementedsecond counter value.